KillCountPhilosophy

There is a very strong chance he has psychopathy (maybe ASPD to be exact). He has no remorse for anything he does if it's in relation to his goals.

That's not to say he is fully uncaring. He likely cares for those who he admires and respects (e.g. high ranking legionaries). But his care is only limited to those individuals. His care comes in the form of strong loyalty.

He is definitely not capable of any true love. If there was anyone he could truly"love", it would be the Caesar and serving the Legion. It's his sole driving force in life. He would happily fight and die for Caesar.

This leads me to believe if he were to ever start liking the courier romantically or sexually, it would be a great, intense obsession for him, instead of love. He would be driven for a desire to control and possess his object of interest.

If you are his object of interest (god, good luck), I think his sadism goes to extremely disturbing lengths. He will not hesitate to do the worst to you, whether it's for his own enjoyment or for Caesar.

I think Vulpes is genuinely the smartest and most quick witted legionary but would do poorer in leading the entire faction, compared to someone like Caesar or Lanius. He's good at leading people in battle related situations, very level-headed and rational, but less so good at being able to build up a very appealing reputation and image for his Legion. He's just too spy-ish and uses deception excessively.

Ignoring his monstrous brutality, if you became close allies with him, he would make an amazing mentor and source of motivation. As I said, he is prone to obsession, so he'd be really passionate about helping someone he deeply respects, and finds himself obsessing over the goals he sets for himself. He's a perfectionist in that regard and wouldn't hesitate to sacrifice any energy or time.